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The adjustment factor found for each duration is used to modify the corresponding rainfall depth for that duration by multiplying these two quantities. Once this step has been completed, all rainfall values have been adjusted for the particular drainage area being studied. 3.5. PARTIAL-TO-ANNUAL SERIES ADJUSTMENT. The previously described rainfall amounts are for partial-duration series of rainfall values. Conversion of rainfall values to an annual series may be needed. This adjustment is applicable only to return periods with a frequency of 10 years or less. The rainfall depth- frequency curve is converted from one for which one or more events per year were used (called a partial-duration series, which is one in which all events above some selected base value are used) to one using only a single event each year (called an annual series. in which the single highest event each year is used, even though the second highest in some years maybe greater than the highest in other years). For economic analysis of agricultural areas, it 'is possible that damages are sustained by flood events that have a probability of occurrence of more than once per year. Where several floods per year are causing significant damage, it would be desirable to use a partial-duration series and not make the adjustment. In many economic analyses, especially in urbanizing areas, these multiple floods (once- or twice-per-year events) do not cause significant damage. Therefore, the adjustment factor would be applied to prevent the use of biased (high) rainfall depths to determine the low end of the frequency curve. The adjustment from partial-to-annual series is performed by multiplying the rainfall depths for each duration by the appropriate conversion factor. The conversion factors are as follows: SERIES 2-YEAR 5- YEAR 10-YEAR FACTOR 0.88 0.96 0.99 No adjustment is needed .for rarer return intervals since the two curves coincide after the 10-year event. At this point, all adjustments have been made. The next step is to proceed through further breakdown and arrangement of the hypothetical storm. 3.6. DIVISION INTO INCREMENTAL VALUES. One now takes the adjusted rainfall values for a particular storm (there are usually six values) and further subdivides these to arrive at a rainfall depth value for each time increment (for example, there will be twenty-four values for the 6-hour-duration 15-minute-interval case). This division into increments is usually performed by plotting the values of rainfall depth (in inches) versus duration (in minutes) on logarithmic paper, fitting a curve through these points. and then reading off accumulated depth values for each 7-16